Melanocytes adhere to and synthesize laminin-5 in vitro

Melanocytes arise from the neural crest, migrate to the skin, and can be de tected in the basal layer of the epidermis in skin biopsies of human fetuse s as early as 11 weeks gestational age. During post-natal life, melanocytes reside at the basal layer of the epidermis, but the ligands to which they attach are unknown. Laminin-5 is a component of anchoring filaments of the lamina lucida of the epidermal basement membrane. In this report we show th at human melanocytes adhere to purified laminin-5 to a level comparable wit h normal human keratinocytes. Blocking antibodies to the 165 kDa subunit of laminin-5 significantly inhibited fetal and neonatal melanocyte attachment to the surface of salt-split skin, which exposes laminin-5 on its surface, suggesting that laminin-5 is a ligand for melanocyte attachment to the bas ement membrane in vivo. Western blotting of concentrated culture supernatan t of fetal and neonatal melanocytes with anti-laminin-5 antibodies demonstr ated a single immunoreactive band of the expected size of laminin-5. In con trast, 3 human metastatic melanoma cell lines did not produce laminin-5. Im munofluorescence microscopy with antibodies to each of the three chains of laminin-5 confirmed the presence of laminin-5 in a peri-cellular distributi on around melanocytes, but not melanoma cells. Our results suggest that lam inin-5 may be a ligand for normal human melanocytes in the basement membran e, and that loss of laminin-5 production by melanoma cells may be a marker for malignant transformation.